package leetcode;

/**
 * 142. 环形链表 II
 */
public class Solution142 {
    public ListNode detectCycle(ListNode head) {
        ListNode fast = head;
        ListNode slow =head;
        while(fast!=null && fast.next !=null){
            fast = fast.next.next;
            slow = slow.next;
            if(fast==slow){
                break;
            }
        }
        if(fast == null || fast.next == null){
            return null;
        }
        slow = head;
        while(fast!=slow){
            fast = fast.next;
            slow = slow.next;
        }
        return slow;
    }
}
